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How far should an object be held from a concave mirror of focal length 40 cm so as to get an image magnified 3 times ?
Verified Answer
How far should an object be held from a concave mirror of focal length...
Focal length, f = -40 cm
Suppose a real and magnified image is formed. Let object distance be –u, image distance be –v.
The magnification is given as, m = -v/u = -3
Therefore, v = 3u
Now using mirror formula,
(-1/40) = (-1/v) + (-1/u)
=> 1/40 = 1/3u + 1/u
=> 1/40 = 4/3u
=> u = 53.3 cm
=> v = 159.9cm from the pole of the mirror.
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Most Upvoted Answer
How far should an object be held from a concave mirror of focal length...
Solution:

Given,
Focal length of concave mirror (f) = -40 cm (negative because it is a concave mirror)
Magnification of the image (m) = 3

We need to find the distance of the object from the mirror (u).

Formula:
The formula for magnification (m) in terms of the distance of object (u) and the distance of the image (v) from the mirror for a concave mirror is:
m = -v/u

The formula for the focal length (f) in terms of the distance of object (u) and the distance of the image (v) from the mirror for a concave mirror is:
1/f = 1/u + 1/v

From the above two equations, we can get the value of v in terms of u and f as follows:
v = -fu/(u-f)

Substituting the values of f and m in the above equation, we get:
v = -120 cm

The negative sign indicates that the image is formed on the same side as that of the object.

Answer:
Therefore, the distance of the object from the concave mirror should be 120 cm so as to get an image magnified 3 times.
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How far should an object be held from a concave mirror of focal length 40 cm so as to get an image magnified 3 times ?
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